Group B streptococci (GBS) or Streptococcus agalactiae are weakly beta-hemolytic, facultatively anaerobic Gram-positive cocci, which have emerged over the past 50 years as the most significant bacterial cause of neonatal sepsis, pneumonia, and meningitis. GBS account for 30-50 percent of neonatal bacterial infections and increases in adult GBS infections have also been noted. This demonstrates that GBS infections remain an important public health problem. We propose to sequence the 2.1 Mb genome of S. agalactiae serotype Ia strain A909 using a genome-wide random shotgun approach. We will then use the final assembled sequence and its complete annotation to perform detailed comparative genomics analyses between serotype Ia and other organisms causing pneumonia and meningitis. These analyses will allow to identify virulence determinants shared by all organisms or specific to individual ones. These determinants will be related to Drs. Jones and Rubens? experiments on signature tagged mutagenesis and TnphoZ translational fusion (identification of secreted proteins) mutant libraries constructed through transposon insertions in strain A909. Regions where transposons inserted will be aligned to the genome sequence to identify the genes affected. A subset of the mutants conserved across serotypes will be analyzed in the rat sepsis model to evaluate their virulence. This collaborative effort will provide extensive preliminary data for future proposals relevant to understanding the pathogenesis of S. agalactiae infections.